The invention relates to an apparatus for removing contact lenses, especially from a mould half.
In an automatic manufacturing process for contact lenses, particularly disposable lenses that are manufactured in large unit numbers, it is necessary to automatically remove the contact lenses from a mould half. Contact lenses, which are to be manufactured economically in large unit numbers, are preferably manufactured by the so-called mould or full-mould process. In these processes, the lenses are manufactured into their final shape between two mould halves, so that there is no need to subsequently finish the surfaces of the lenses, nor to finish the edges. Mould processes are described for example in PCT patent application no. WO/87/04390 or in EP-A 0 367.513.
The contact lenses produced in this manner are moulded parts having little mechanical stability and a water content of more than 60% by weight. After manufacture, the lens is metrologically checked, then packaged and subjected to heat sterilisation at 121xc2x0 C. in an autoclave.
In these known mould processes, the geometry of the contact lens to be manufactured is defined by the mould cavity. The edge of the contact lens is likewise formed by the mould which normally consists of two mould halves. The geometry of the edge is defined by the contour of the two mould halves in the area in which they make contact.
To manufacture a contact lens, first of all a certain amount of the fluid starting material is placed in the female mould half. Afterwards, the mould is closed by placing the male mould half thereon. Normally, a surplus of starting material is used, so that, when the mould is closed, the excess is expelled into an overflow area adjacent to the outer mould cavity. The subsequent, polymerisation or crosslinking of the starting material takes place by radiation with UV light, or by heat action, or by another non-thermal method.
Subsequently, the contact lenses thus produced must be removed from the mould halves, preferably from the female mould halves. To do this, a gripper is provided for example. This is moved in the direction of the mould half and removes the lenses from the mould half by applying suction to the lenses with a vacuum. After removing the lenses, the gripper arm moves into another position, so that further procedures can be carried out, such as drying of the contact lenses on the gripper, checking of the contact lens using an image-processing system, placing the contact lenses in a package, and rinsing and drying of the gripper itself. To this end, the gripper may be, for example, star-shaped, and in this configuration represents the connecting link between manufacturing the contact lenses and primary packaging. Only the lenses that are centred by the gripper and grasped smoothly can be checked by the image-processing system and subsequently deposited in the package. Thus, the accurate removal of lenses by the gripper is an essential prerequisite to attaining a high yield of the apparatus.
Usually prior to removal from the mould half, the contact lenses are first of all loosened and, if desired, also inverted from the male to the female mould half, since the actual removal of the contact lenses is preferably effected from the female mould half. To enable the apparatus to be operated most economically, several mould halves, preferably a figure of 10, can be held in one tool and grasped together by one gripper arm, which accordingly has 10 grippers.
To remove the contact lens from such a tool, the gripper arm moves downwards. The contact lens is suctioned onto the gripper by a vacuum. To remove the contact lens, a vacuum of ca. xe2x88x920.3 bars (measured on the gripper) is required. The distance d between a gripper and a mould half, which is measured between the contour edge of a mould half and the end face of the gripper, should be preferably more than 0.5 mm, since otherwise damage may occur on the gripper or on the mould half. In order to ensure an exact adjustment of the gripper over the females mould halves in question, the gripper is aligned by moving towards the stop of the contour edge of the mould half, then elevated by a specific amount and subsequently fixed. However, this is extremely complex and relatively prone to errors.
The invention is based on the problem of increasing the distance between the gripper and the mould half whilst maintaining the gripping power, so as to avoid damage to the contact lenses and the mould half, and of enabling the gripper to be simply aligned in relation to the mould half. In addition, servicing of the apparatus should be simplified.
The invention solves this problem with the features indicated in claim 1. As far as further essential refinements are concerned, reference is made to the dependent claims.
By inserting a spacer which is placed between the mould half and the gripper, it is no longer necessary to exactly align the gripper in relation to the mould half, thereby enabling simpler servicing and assembly of the gripper to take place. In addition, there is improved centring of the contact lenses on the gripper, thus increasing accuracy of image processing.